The insensitivity to insulin—and the resulting metabolic disruption—is caused by persistently high blood sugar levels. IR can trigger and worsen various diseases, such as EMS, laminitis, Cushing's disease, and sweet itch.

Low-Sugar Diet

For horses with IR, a diet low in sugar and starch is recommended. If your horse is overweight, has a cresty neck, or frequently rubs its mane and tail, it's wise to avoid sugary feeds. This means: as little grain and concentrate as possible. Instead, the diet should mainly consist of roughage like hay (and possibly low-sugar grass), as roughage causes far smaller spikes in blood sugar. Regular exercise is also important to stimulate fat metabolism and improve insulin sensitivity. This includes both free movement and structured training—on the ground, under saddle, or in harness.

Be Careful with Concentrates

Feeding low-sugar starts with avoiding traditional concentrates, which are often high in sugars, starch, and molasses. Read the labels carefully—there are now many alternative feeds available with significantly lower sugar content. You can also opt for just a balancer pellet to meet your horse’s vitamin and mineral needs, and skip concentrates altogether.

Be Careful with Grass

Grass is tasty, but it can also be very high in sugar—especially in spring and autumn when temperatures drop below freezing at night and the sun shines on the grass during the day. Grass that is grazed too short or is under stress can also contain high sugar levels. A pasture full of perennial ryegrass is not suitable for horses, as this grass type is very rich. There are other grass mixtures available that are much better suited to the needs of horses. Also, avoid treating your pasture with artificial fertilizers, as these can significantly raise sugar levels as well. Easy-keeper breeds like Tinkers and Shetland ponies should ideally not have unlimited access to lush pasture. But even with other horses, caution is advised. For example, only let them out once fructan levels are lower (later in the morning), and make sure they’ve had some hay before grazing.

Test Your Hay

If your horse is sensitive to IR, it may be wise to have your hay tested. In recent years, Dutch hay has often been very high in sugar. There are major differences between batches. For an IR-sensitive horse, always choose dry, long-stemmed, and low-sugar hay.